What are common reasons for PHP not being able to calculate cosine correctly?

One common reason for PHP not being able to calculate cosine correctly is due to incorrect input values being passed to the cosine function. Ensure that the input values are in radians if using the `cos()` function in PHP. Another reason could be due to using the incorrect function or not properly including the necessary math library. Make sure to use the `cos()` function from the `math` library in PHP.

// Incorrect way of calculating cosine
$angle_degrees = 45;
$cosine_value = cos($angle_degrees); // Incorrect: input should be in radians

// Correct way of calculating cosine
$angle_radians = deg2rad(45); // Convert degrees to radians
$cosine_value = cos($angle_radians);
echo $cosine_value;